圆柱的直径为60cm,重3kN,由于力P作用而沿水平面作匀速运动。已知滚阻系数δ=0.5cm,而力P与水平面的夹角微α=30o,力P的大小为( )N。
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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